We present the numerical solutions of the coupled-mode equations describing all-optical switching of a fiber grating by a pump pulse detuned from the Bragg condition. The width of the pulse is shorter than the length of the grating. The results reveal that copropagating and counter-propagating pump-probe configurations lead to different switching characteristics. Furthermore, an initial detuning of the probe team is found to improve the switching. These calculations are compared to experimental results previously published.